In vivo models are essential for understanding the pathogenesis of infectious diseases. The SCID-hu mouse implanted with human fetal liver and thymus allows normal human thymopoiesis to take place for up to one year. HIV infection of SCID-hu mice results in severe depletion of CD4-bearing thymocytes. The investigators propose to use this model to study how administration of cytokines can influence HIV pathogenesis and immune reconstitution in the human thymus. The investigators will determine which cytokines are involved in regulating T-cell development and HIV production. The investigators will also perform experiments to determine if cytokine treatment can augment renewed thymopoiesis from precursor cells following HIV- induced depletion. Additional studies will assess whether cytokine administration can augment certain antiretroviral chemotherapeutic approaches and stem cell immune reconstitution strategies in vivo. These studies will help to comprehend how HIV infection negatively influences immune function, and may eventually lead to novel therapeutic strategies to treat HIV infection.